Orthopedic casts for use in treating bone fractures or other conditions requiring immobilization of a body member are generally formed from a sheet of fabric or scrim material coasted or impregnated with a substance that hardens into a rigid structure after the sheet has been wrapped around the body member.
Many orthopedic casts now commonly used are comprised of a backing impregnated with a water-curable isocyanate-functional prepolymer. The backing can be a knitted, woven, or nonwoven scrim comprised of natural, polymeric, or glass fibers. The preferred scrim materials are knitted fiberglass scrims. These casts when cured have a higher strength to weight ratio than plaster-of-paris, are more resistant to water and provide good radiolucency.
U.S. Pat. No. 4,411,262 (von Bonin), U.S. Pat. No. 4,502,479 (Garwood), and U.S. Pat. No. 4,667,661 (Scholz, et al.) disclose water-curable isocyanate-functional prepolymers useful in orthopedic bandages. The prepolymer typically includes a tertiary amine catalyst in an amount selected to optimize the "set" time. After the resin-impregnated scrim has been immersed in water, sufficient "working time", e.g., 3 to 5 minutes, should be provided in which the wrapping is accomplished and the cast is manually molded into a desired shape. However, after the cast is shaped, the resin should continue to harden and rapidly build strength, typically in 15-30 minutes, into a rigid, high-strength, weight-bearing cast.
U.S. Pat. No. 4,376,438 (Straube et al.) discloses an orthopedic casting material wherein the tertiary amine catalyst is incorporated into the backbone of the polymer portion of the isocyanate-functional prepolymer. No separate catalyst is required
U.S. Pat. No. 4,502,479 (Garwood et al.) discloses the use of tertiary alkanolamines, e.g., dimethylethanolamine, as catalysts in the curing of a water-curable isocyanate-functional prepolymer. At concentrations that do not adversely affect shelf stability, these catalysts do not cure as fast as desired by many experienced cast appliers.
U.S. Pat. No. 4,433,680 (Yoon) discloses the use of 2,2'-dimorpholinodiethyl ether (DMDEE) as a catalyst in the cure of a water-curable isocyanate-functional prepolymer on an open-weave fibrous substrate to form an orthopedic bandage.
U.S. Pat. No. 4,705,840 (Buckanin) discloses the use of 2,2'-dimorpholinyldialkyl ethers substituted on one of the carbon atoms alpha to the central ether oxygen atom as catalysts in the curing of water-curable isocyanate-functional prepolymers.